This invention relates to a roll sheet feeding device, wherein a lengthwise sheet in a roll form may be cut at a desired length selected from several kinds of predetermined lengths.
In a prior art, roll sheet feeding device for use in a copying machine, wherein the lengthwise sheet in the roll form is cut by a given length and a cut sheet is automatically fed to a succeeding step, there has been adopted a process for cutting the travelling roll sheet by a given length without interrupting the travelling. More in detail, the process has been such that, during copying operations, a sheet feed roller is started at a given timing so as to feed a roll sheet, and when the roll sheet is fed by a length commensurate to the length of an original, a cutter is operated to cut the roll sheet by a given length. With such a process in which a cutter is operated while the roll sheet is being travelled, no substantial problem arises so long as a sheet feeding speed is low. If, on the other hand, the cutting timing of the cutter is shifted only to a small extent in the case of a high feeding speed, this small shift leads to a large variation in length of sheet cut, thus resulting in a large difference or error in length of cut sheet. Futhermore, the operation of the cutter would badly affect the travelling of the roll sheet, particularly in an image-formed area thereof, thus causing a blurred image.
With a view to solving the above drawback, an attempt has been proposed, in which the roll sheet is stopped to be cut by a given length immediately before the cutter is put into operation. In such a device, a sheet path between a sheet feeding station and an image forming station need be curved for slackening the roll sheet, in order that the sheet travels smoothly, particularly in an image-formed area of the sheet, so as to prevent formation of a blurred image. Such a device, however, impairs accuracy in performance of a mechanism for controlling the starting and stopping of the roll sheet, namely in engagement and disengagement of a clutch for starting and interrupting the sheet feed roller.
The prior art device of the type incorporates a clutch mechanism as shown by way of example in FIG. 1. A drive-side boss 1 and a driven-side or idler side boss 2 are mounted on a common shaft adjacent to each other. Drive-side boss 1 has a diameter larger to some extent than driven-side boss 2. A coil spring 3 is wound on drive-side boss 1 and fixed thereto. Part of coil spring 3 is wound also on driven-side boss 2 with a small space between the coil spring 3 and the outer periphery of the driven-side boss 2, because the diameter of boss 2 is smaller than that of drive-side boss 1. A brake ring 5 operated by a solenoid 4 is fitted on the left extremity (in FIG. 1) of coil spring 3 on the driven-side boss 2, so that a braking action may be applied to coil spring 3 when solenoid 4 is energized. A direction of turns of coil spring 3 on the driven side is opposite to the rotating direction on the driving side. If solenoid 4 remains inoperative, drive-side boss 1 on the driving side and spring 3 on the driving side are integrally rotated, with driven-side boss 2 remaining stationary. When solenoid 4 becomes energized, then brake ring 5 is pulled to apply a braking action to the left extremely of coil spring 3 wound on the driven side. Coil spring 3 is thus coiled fast round the driven-side boss, with the resultant reduction in diameter of the driven-side spring, thus allowing driven-side boss 2 to rotate. When the activation of solenoid 4 is interrupted, brake ring 5 resumes its home position, and coil spring 3 becomes loose, whereby the rotation of the driven-side boss 2 is interrupted. If a sheet feed roller is connected to boss driven-side boss 2, then travel of a sheet may be started or interrupted by making solenoid 4 conducting or non-conducting.
The clutch so far described, however, involves many unstable factors in the process leading from the operation of solenoid 4 to the winding of coil spring 3 on the driven-side boss 2, and particularly, a duration of time from the operation of solenoid 4 to the starting of driven-side boss 2 is liable to change due to variation in coefficient of friction. This could be avoided by providing an increased force to solenoid 4, yet resulting in an increased loss in driving force, as well as increased wear of brake 5. Furthermore, in case that solenoid 4 is stopped to interrupt the rotation of the driven-side boss 2, there occurs various indefinite factors, such as a frictional force and inertia on the driven-side, until rotation on the driven-side is stopped, and such constitutes decisive factors to make variable a duration of time from the deenergization of solenoid 4 to the stop of the driven-side boss 2. Because of the failure of providing an accurate timing between the operation of solenoid 4 and the starting and stopping of the driven-side boss 2, a position at which the sheet stops cannot be controlled in an accurate manner, resulting in the lowered accuracy in cut length of the sheet, particularly in case that a sheet feeding speed is high.